It is well known that maintenance of a comfortable environment requires control not only of the air temperature in the environment but also the relative humidity of the air. Air cooling systems for reducing and maintaining the air temperature at comfortable levels within an enclosed space are common. When ambient temperatures are relatively high, such systems can also dehumidify the air, for in cooling the air in the space to a comfortable temperature, the system also lowers the temperature of conditioned air to below the dew point of the air and moisture in the air condenses out.
However, conditions may exist where air in the space is at a comfortable temperature (i.e. in the range of 70.degree. to 75.degree. F.) (21.degree. to 24.degree. C.) but the relative humidity remains uncomfortably high. In these conditions, a conventional cooling system is capable of dehumidification only by further cooling the air in the space, thus lowering the temperature to a level that is not comfortable to the occupants.
Many efforts have been taken to overcome this shortcoming in conventional air cooling systems. One solution has been to provide a separate dehumidifying apparatus in the space.
Another approach has been to use an air cooling system to cool the air to lower its dewpoint and dehumidify it, then reheat it to a temperature that is within the comfort range. This reheating step has been accomplished in some designs by electric resistance heat. Still other designs of air conditioners of the vapor compression type have routed hot refrigerant from the discharge of the system compressor to a reheat heat exchanger located so that air that has first been cooled by the evaporator section of the system is warmed by a reheat heat exchanger before being directed to the space.
Most if not all of such hot refrigerant reheat designs have used two separate heat exchangers configured in a series relationship with respect to the air flow through them.